The present invention relates to a portable printer having automatic print alignment, and particularly to a portable printer having automatic print alignment in accordance with the width of a roll of paper or label stock centered in the printer. The portable printer provides for locking the centered position of the roll when a cover for accessing the roll in the printer is closed and unlocking the position of the roll when the cover is opened.
Conventional portable printers use a roll of wound stock material, such as paper or label stock, which is loaded into the printer such that the paper from the roll will properly feed and align with a thermal print head for printing. These rolls may be in different widths such that labels or different widths may be printed.
A roll may be side-loaded and centered onto a spindle as shown in U.S. Pat. No. 5,860,753, or top-loaded and centered, as in the label printer manufactured by Zebra Technologies, Corp., Camarillo, Calif., model no. P2242. Printers providing for a top-loaded roll have a cavity to receive the roll and two rotatable spindle members are urged by spring or springs into the tubular core of the rolls into a centered position with respect to the print head of the printer. One problem with top-loaded portable printer is that when the printer is dropped or otherwise receives an accidental impact, the roll can disengage from the spindle members, negatively impacting printer function or require the operator to reset the roll between the spindle members.
Regardless of the loading approach used, the print head of a typical portable printer is of a length sufficient to print the widest paper for that printer so as to accommodate the range of roll widths. When rolls are of a width less than the print head length, the print head""s width exceeds the paper width. Typically, the user of the portable printer must assure that the roll is of a proper width for the information to be printed, otherwise the printing may extend beyond one or both sides of the paper from the roll, or from one side of the roll from a non-centered roll. Examples of portable printers with non-centered rolls are shown for example in U.S. Pat. Nos. 5,267,800 and 5,447,379. Thus, printing elements of the print head may be utilized corresponding to areas outside the width of the roll, which over time will likely damage the print head. This damage is due to heat buildup by printing elements that are not in contact with the paper, and therefore, not able to transfer heat to the paper. Thus, it is desirable to automatically align printing by a portable printer with the width of the roll.
In larger ink jet printers a reflective sensor may be provided under the carriage for detecting the width of sheets of paper transported from a stack of paper. Such ink jet printers, are described, for example, in U.S. Pat. Nos. 5,398,049, and 6,007,184. A paper width detector LED and paper width sensor are described in the ink jet printer of U.S. Pat. No. 6,193,344. However, such ink jet printers due to their weight or size cannot be practically worn or hand carried and are not part of any centering mechanism for a roll.
It is an object of the present invention to provide a portable printer for printing on a roll of paper or label stock having automatic print alignment with the width of the roll, thereby preventing printing outside the width of the paper from the roll.
It is another object of the present invention to provide a portable printer having a centering mechanism for a roll in which the centering mechanism can be locked to prevent accidental disengagement of the roll from the centering mechanism when a cover for accessing the roll is closed.
A further object of the present invention is to provide a portable printer having a removable wireless (RF) communication module.
Briefly described, the portable printer embodying the present invention has a housing having a compartment for receiving the roll, a cover to access the roll, and a centering mechanism for the roll. The centering mechanism has two rotatable spindle members in the compartment engageable with the opposing ends of the roll""s tubular core, and a pair of racks which are each coupled to one of the spindle members by an edge guide arm, and to each other by a gear, to enable the spindle members to move in opposite directions with respect to a center between the spindle members. The position of centering mechanism with respect to the roll""s width is optically encoded by indicia on one of the racks with respect to a fixed sensor capable of illuminating and reading a portion of the indicia representative of the encoded position of the rack having the indicia and of the roll width. A controller in the housing automatically aligns printing with respect to the roll""s width in accordance with the encoded position read by the sensor.
In an alternative embodiment to the optical indicia and sensor, the position of centering mechanism with respect to the roll""s width is magnetically encoded by a magnet on one of the racks or edge guide arm with respect to a magnetic sensor in the housing capable of detecting the level of the magnetic field (and/or polarity) of the magnet which changes in accordance with distance (and/or position) of the magnet with respect to the sensor, thereby enabling the sensor to provide a signal representative of the encoded position of the centering mechanism with respect to the roll""s width. In another alternative embodiment, an electromechanical position encoder is used with the wheel which mechanically encodes the position of the centering mechanism with respect to the rotationally movement of one of the racks or the gear, and outputs a value to the controller representatively of the position of the centering mechanism with respect to the roll""s width. In a further alternative embodiment, a resistive strip replaces the indicia and a voltage is applied to the strip, such that a fixed sensor provided by a electrical wire or wiper reads the voltage signal from the strip. As wiper reads different locations along the strip, different voltage signals are provided and these signals are representative of the encoded position of the centering mechanism with respect to the roll""s width.
A locking mechanism may be coupled to the centering mechanism to lock the centering mechanism when the cover is closed to prevent movement of the gear and the spindle members and racks coupled thereto. The locking mechanism includes a pivotable lock actuator which pivots as the cover is opened and closed, and a gear lock member coupled to the lock actuator, in which the gear lock member engages the gear of the centering mechanism to lock the rotation of the gear when the lock actuator pivots in a first direction in response to the cover being closed, and disengages the gear when the lock actuator pivots in an opposite direction when the cover is opened. The lock actuator pivots in response to a pivotable latch member which rotates the lock actuator to lock the cover when closed, which and when released, allows an operator to open the cover to access the roll compartment.
The portable printer may further have a removable RF communication module accessible through an opening in the printer""s housing for connection with the controller to enable communication with a host terminal or computer system.